1. Field of the Invention
The present invention relates to a method for manufacturing a flexible device, a flexible device, a flexible piezoelectric device and a flexible capacitor manufactured by the same, and a method for manufacturing a flexible sensor. More particularly, it relates to a method for manufacturing a flexible device wherein a metal oxide layer formed on a silicon substrate is etched rather than etching the silicon substrate itself and then a device formed thereby is separated from the substrate, thus being capable of preventing damage of the silicon substrate and saving the cost of using the expensive single-crystal silicon substrate, a flexible device, a flexible piezoelectric device and a flexible capacitor manufactured by the same, and a method for manufacturing a flexible sensor.
2. Description of Related Art
As the era of ubiquitous information technology providing required information and services anywhere and anytime without restrictions draws near, the need on flexible displays that can be conveniently used in various living environments is on the increase. Thus, researches are performed in many fields to realize such flexible displays. Especially, researches on use of nanomaterials such as nanowire (NW), carbon nanotube (CNT), etc. or organic semiconductors are drawing a lot of attentions. In 2001, Bell Labs first succeeded in developing a flexible display using an organic semiconductor. However, these materials do not have superior electrical properties (The effective mobility of an organic semiconductor and a nanowire is in the order of ˜1 cm2/V and ˜5 cm2/V, respectively.) and there are many difficulties in commercialization because of difficulty in material homogeneity and processing. To solve these problems, a printable microstructure semiconductor (μs-Sc) was invented in 2004 by Illinois Institute of Technology (Appl. Phys. Lett. 84, 5398, 2004, hereinafter “Prior art 1”).
According to Prior art 1, single crystal silicon having excellent device performance is directly detached from a bulk silicon substrate and the resulting microstructure semiconductor is transferred to a flexible substrate by means of soft lithography. The device manufactured by transferring a single-crystal microstructure semiconductor to a plastic substrate shows the most excellent electrical performance among all existing flexible electronics devices (IEEE Electron Device Lett., 27, 460, 2006).
To describe Prior art 1 in more detail, a microstructure semiconductor is designed into a dumbbell shape, a bottom side thereof is etched to form a support, and then the microstructure semiconductor is detached using a polydimethylsiloxane (PDMS) stamp to selectively transfer the microstructure semiconductor at the wanted position. Prior art 1 is advantageous not only in that a device can be manufactured on a wanted location of a plastic substrate through selective transfer but also in that the microstructure semiconductor remaining on the silicon on insulator (SOI) substrate without being transferred may be used for other applications, thereby saving processing cost.
However, Prior art 1 is associated with the problem that an expensive silicon substrate having (1, 1, 1) crystal structure has to be used to accomplish selective etching of the silicon substrate (i.e., in the horizontal direction). Further, since Prior art 1 involves etching of the silicon substrate itself, the silicon substrate is consumed gradually along with the process. Recycling of the silicon substrate is practically difficult because it should be planarized through, for example, chemical-mechanical polishing.
In general, existing electronic devices are manufactured on a hard silicon substrate. It is because the manufacture of the devices usually requires a high-temperature semiconductor process. However, the limitation of the device substrate is problematic in that applications to piezoelectric devices, solar cells, etc. are restricted. Especially, the limitation of the substrate limits application to piezoelectric devices. A piezoelectric device refers to a device exhibiting piezoelectricity. Crystals of quartz, tourmaline, Rochelle salts, etc. have long been used for piezoelectric devices. Recently developed artificial crystals such as lead zirconate titanate, barium titanate (BaTiO3, BTO), ammonium dihydrogen phosphate and ethylenediamine tartrate show excellent piezoelectricity and may be made to have better piezoelectric property through doping. The piezoelectric device generates electricity in response to applied pressure. If the piezoelectric device is applied to a flexible substrate that may be bent naturally, the bending property of the flexible substrate may be converted into an electric energy. However, at present, there is no piezoelectric device, particularly piezoelectric device with a large area, applied to a flexible substrate. Further, in general, an additional charging means is provided outside a BTO device to store the generated electric energy, which inevitably increases the size of the device in which the piezoelectric device is used. Furthermore, although use of a BTO device with a large area is preferred to produce a large quantity of electric energy, it is impossible to apply the large-area piezoelectric device to a flexible substrate with the current technology. In addition, although the charge generated from the piezoelectric material layer is not uniform, there has been no attempt to adopt an electronic device such as a capacitor to smooth it.